Rotary electric machines, operable as motors and power generators, include, for example, a rotor rotatable about a preset axis and a stator disposed around the rotor. The stator is comprised of a stator core and a stator coil provided in the stator core. One or more conductive wires are wound in the stator core in many turns to form the stator coil. Both portions (many turn portions) of the stator coil, axially projecting from the stator core, provide cylindrical coil ends.
When current flows through the stator coil, heat is generated from the stator core and/or the stator coil. The generated heat affects on magnetic flux generated in the rotary electric machine; this may reduce the efficiency of the rotary electric machine. In light of this problem, rotary electric machines with specific cooling structures have been proposed, an example of which is disclosed in Japanese Patent Application Publication No. 2005-12961.
An example of these cooling structures is configured such that an insulative coolant, such as oil, flows along the stator coil. For example, the aforementioned Patent Application Publication discloses such a rotary electric machine disposed in a vehicle with its axial direction orthogonal to the height direction of the vehicle. The rotary electric machine is comprised of a groove formed in the outer circumferential surface of each coil end. When a coolant, such as oil, is supplied into a top portion of the groove, the groove guides the coolant therealong so that the coolant falls along the outer circumferential surface of each coil end.